.300 Whisper

The .300 Whisper, displayed center.

Type

Rifle

Place of origin

United States

Specifications

Parent case

.221 Fireball/.223 Remington

Case type

Rimless, Bottleneck

Bullet diameter

7.62 mm (0.300 in)

Neck diameter

8.46 mm (0.333 in)

Shoulder diameter

9.14 mm (0.360 in)

Base diameter

9.54 mm (0.376 in)

Rim diameter

9.60 mm (0.378 in)

Rim thickness

1.14 mm (0.045 in)

Case length

34.90 mm (1.374 in)

Overall length

57.00 mm (2.244 in)

Rifling twist

203 mm (1 in 8 in)

Primer type

Small rifle

Ballistic performance

Bullet mass/type	Velocity	Energy
125 gr (8 g) JHP	2,100 ft/s (640 m/s)	1,224 ft·lbf (1,660 J)
220 gr (14 g) JHP	1,040 ft/s (320 m/s)	529 ft·lbf (717 J)

Test barrel length: 16 in
Source(s): CIP specifications COR-BON Ammunition

The .300 Whisper is a CIP standard cartridge in the Whisper family, a group of cartridges developed in the early 1990s by J.D. Jones of SSK Industries. It was developed as a multi-purpose cartridge, capable of utilizing relatively lightweight bullets at supersonic velocities as well as heavier bullets (200–250 grains) at subsonic velocities.

.300 Whisper is also sometimes known as .300 Fireball or .300-221, but there is some variation in dimensions and pressure between these cartridges. Some implementations of .300 Whisper meet the SAAMI specifications for 300 AAC Blackout. As of 2016, there is no CIP specification for the latter and no SAAMI specification for the former, leading to assumptions of these two being interchangeable, which is not true in all cases.

The .300 Whisper was originally based on the .221 Fireball case necked up to .30 caliber. However, avid reloaders have found the .223 Remington or 5.56×45mm NATO works well when shortened and resized to .30 caliber. Firing in the .300 Whisper chamber results in a slightly sharper shoulder. Magnum pistol powders such as H110 work well for supersonic loads. Sierra 240 grain (16 g) jacketed bullets work well if the barrel has a 1:8 twist. Barrels with a 1:10 twist will stabilize 220 grain (14 g) bullets at subsonic speeds. 125 grain (8 g) bullets will reach 2400 ft/s (730 m/s).

There are a few points to be considered regarding the utility of the .300 Whisper:

In addition to special applications in suppressed firearms, the .300 Whisper has become popular with metallic silhouette shooters due to its low recoil, good long range performance, and very high accuracy.

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Wikipedia